Personality or individual consistency in behavioural responsiveness to stimuli and situations, is recognized in a wide range of animal species, including dogs. These traits are important for determining how well a dog fits its role (e.g. as pet or working dog) and can also influence the dog’s psychological well-being. The distinct behavioural characteristics of individual dog breeds suggest a strong genetic component to personality in this species and there is also evidence for within-breed variation. However, it is a challenge to gather sufficiently large datasets to dissect the genetic basis of complex traits such as behaviour, which are both time-consuming and logistically difficult to measure, and known to be influenced by non-genetic factors. In this study, we exploited the knowledge that owners have of their own dogs to generate a large dataset of 12 personality traits in Labrador Retrievers, the most popular breed in the UK and various other countries. While accounting for key environmental factors, we demonstrate that genetic variance can be detected for dog personality traits assessed using questionnaire data. We identified substantial genetic variance for several traits, including fetching tendency and fear of loud noises, while other traits, such as owner-directed aggression, revealed negligibly small heritabilities. For comparison, an alternative set of 14 traits developed in previous studies were also analysed; differences between the heritabilities of corresponding traits in the two sets indicate that the method of grouping questionnaire data into behavioural factors may influence estimates of heritability. Genomic analyses indicated that these traits are mainly polygenic, such that individual genomic regions have small effects, and suggested chromosomal associations for eight of the traits. Our results demonstrate that dissection of genetic and non-genetic factors that influence dog personality traits can be facilitated using data provided by owners.